White Cornwall Electronics digital thermo-hygrometer without probe, LCD screen and buttons on the front

White Cornwall Electronics digital thermo-hygrometer with its remote probe on the end of a cable

Min-max thermometer hygrometer, with or without probe

Name: Min-max thermometer hygrometer, with or without probe
Brand: Cornwall Electronics
SKU: TK-CORNWALL-THERMOHYGRO
Price: 12.0 USD
Availability: InStock

$12.00

This digital thermo-hygrometer shows the air temperature and relative humidity on its screen, whether placed flat or hung on the wall of a greenhouse, a grow tent or a seedling room. The version with a 3 m probe also reads the temperature at a second location and stores the minimum and maximum readings.

Ref. TK-CORNWALL-THERMOHYGRO·Thermometer

Version : Sans sonde

Sans sonde

Avec sonde de 3 m

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The summary

The device supplied: a Cornwall Electronics digital thermo-hygrometer, with or without its 3 m probe.
The display: the temperature and relative humidity of the air around the device.
The remote probe: a second temperature, taken up to 3 m from the display.
The memory: the minimum and maximum values, on the version with a probe.
In aquaponics: spotting the humid nights when grey mould threatens, above warm water.
In the nursery: checking that lettuce seedlings germinate below 25 °C.

Air temperature and humidity, optional 3 m remote probe

This Cornwall Electronics digital thermometer-hygrometer displays the air temperature and humidity of a greenhouse or grow tent. Without the probe, it measures from -10 to 50 °C; with its 3 m probe, it reads a second point and records the minimum and maximum values. It measures the air, never the water in the fish tank.

In a greenhouse, the temperature changes sharply between the end of the night and the early afternoon, and these swings go unnoticed by anyone who only visits once a day. This digital thermo-hygrometer continuously displays the air temperature and relative humidity on its liquid crystal screen. You can lay it flat on a shelf or hang it on the wall at the height of your plants, and read at a glance the condition of the air around them.

🌡️ With or without a probe

The version without a probe measures the air where it sits, from -10 to 50 °C and from 20 to 95% relative humidity. It suits a seedling room, a small greenhouse or a grow tent, where a single measuring point is enough to monitor the conditions. The version with a probe adds a remote temperature probe, mounted on the end of a 3 m cable, so you can monitor two locations at once: the air near the display and a second point further away, at the other end of the greenhouse or at ground level.

This probe version also records the minimum and maximum temperature and humidity values. In the morning you can see the lowest temperature reached overnight, when nobody was watching, which tells you whether a greenhouse heater held its setpoint or whether the young plants suffered a cold snap. The casing measures 11 x 7 x 2 cm and runs on one AAA battery, supplied with the device.

The probe level with the seedling trays

Slip the probe under the lid of a germination tray and leave the display on the neighbouring shelf. You can then read the temperature actually surrounding the seeds without lifting the lid, and so without losing the humidity that has built up inside. The difference from the room air tells you at once whether germination is taking place in the warm, or whether the tray would benefit from being moved closer to a heat source.

🐟 The air in an aquaponic greenhouse

Air reading

The device measures the air above the crops, where leaf growth and the risk of disease are decided.

Water kept separate

Tank water is monitored with a submersible thermometer, such as the suction-cup model fixed against the wall.

A display distorted by direct sunlight

Placed in full sun or against a heated wall, the screen shows a temperature well above that of the air your plants breathe. Install the device in the shade, away from heaters and out of reach of watering splashes, as it is designed for indoor use.

An aquaponic greenhouse holds hundreds of litres of water that evaporate day and night, and plants that transpire in their turn. In the evening, as the air cools, the relative humidity rises without a single drop being added, because air at 21 °C can hold twice as much water vapour as air at 10 °C. All this vapour then settles on the cold walls, on the plastic film and on the leaves. This is the moment the hygrometer makes visible, and the maximum-reading memory of the probe version confirms it for you the next morning.

The reading has a practical consequence. Grey mould, Botrytis, infects foliage that stays wet for 8 to 12 hours at a relative humidity of 93% or more, between 13 and 18 °C, exactly the conditions of a greenhouse cooling down above still-warm water. If the screen regularly shows more than 90% in the early morning, ventilate at sunset and sunrise, or set up air circulation above the grow beds. The remote probe, placed near the tank, also shows whether the area above the water stays warmer and more humid than the rest of the structure.

🌱 Nursery and young plants

The FAO guide recommends germinating seeds in a separate nursery, in rockwool or coconut fibre, and only transplanting the seedlings into the system at least two weeks after their first true leaves appear. During these weeks, temperature matters more than anything else. Lettuce germinates best between 15 and 20 °C, and above 25 °C its seeds go dormant and stop sprouting. With the probe slipped under the lid of the tray, you can tell whether a sowing of summer lettuces is sitting in heat that blocks it, and move it to a cooler spot before concluding that the seeds are faulty.

🔧 Positioning and reading correctly

Place the display in the middle of the greenhouse, at leaf height, in the shade of a shelf or under a small ventilated shelter, and run the probe out to the spot that matters most to you: a tray of seedlings, the coldest corner, or the soil near the door. Note the recorded extremes each morning: within a week you will know the real temperature range of your structure and the times of day when you need to ventilate or heat. Visible condensation on the plastic confirms a high reading, since at 85% humidity and 15.5 °C, water starts to condense as soon as a surface drops to around 12.8 °C. Replace the AAA battery as soon as the display starts to fade.

Technical specifications

The measurement

Parameters: Temperature and relative humidity
Without probe: -10 to 50 °C, 20 to 95%
With probe: -30 to 70 °C, 25 to 90%
Memory: Minimum and maximumOn the version with a probe

The device

Remote probe: 3 m cableVersion with probe
Screen: 4 x 3 cm LCDVersion with probe
Housing: 11 x 7 x 2 cmVersion with probe
Fitting: Flat or wall-mounted

In the box

1 Cornwall Electronics digital thermo-hygrometer
1 probe on a 3 m cable and 1 AAA battery, in the version with probe

Values from the brand and its distributor for both versions. Humidity and condensation benchmarks from the Universities of Massachusetts and Connecticut; lettuce germination from a seed supplier.

Manufacturer and product safety

Manufacturer: Cornwall Electronics

Information provided under Regulation (EU) 2023/988 on general product safety.

Estimate your
delivery time

This thermo-hygrometer is shipped as a small parcel from a distributor's French warehouse. The exact shipping cost is shown in the basket.

Frequently asked questions

6 questions

6 key questions

Which version should you choose, with or without a probe?

Version	Measuring points	Ranges
Without probe	The air around the display	-10 to 50 °C, 20 to 95%
With 3 m probe	The air around the display and a second point, with memory of the extremes	-30 to 70 °C, 25 to 90%

The version with a probe stores the minimum and maximum readings, which you check in the morning to find out how the night went. It is useful whenever you want to monitor a tray of seedlings, a cold corner or the outside of the greenhouse in addition to the ambient air.

Where should the device be placed in a greenhouse?

Can the probe go into the tank water?

What humidity should you aim for with seedlings?

At what humidity does an aquaponic greenhouse become a risk?

Why does humidity rise at night when nothing has been watered?

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Min-max thermometer hygrometer, with or without probe

The summary